Frame Bond cable run

[itty]

I'm not saying its wrong but why is it assumed that the bonding needs to be 10mm? The array is (generally) not extraneous.

Good point which would bring the armouring of swa back into play!

This reminds me of the eighties when no one really understood extraneous metal work and bathroom bonding. Some sparks ended up bonding metal window frames for heavens sake.

I'm starting to believe that the armour is a method that shows willing and would still be overkill for the potential likely currents. Anyone else agree?

Cheers

 

[BruceB]

Well I am arguing for something here I only half believe in (the DTI Guide) but here goes:
- the DTI guide says 10mm2
- where you have PME then 7671 says 10mm2 for bonding
- if not PME then apply the rules to work out bonding conductor sizes

Of course if you do not believe it is a bonding conductor, but is a cpc then different answers will appear.
Regards
Bruce

 

[itty]

I 'think' because of the lack of galvanic isolation means the potental of the pv modules with respect to earth can be varying and you get the capacitive coupling effect. I have not read the document I mentioned for a while. I suggest you do and then you will be wiser than most of us on the point.

I will read it if I can find it, but assuming you're right the email below from SMA would negate the need for bonding on their TL inverters.

If the Inverter is provided with a Type B RCD, i.e. an RCD that can operate effectively with DC saturated currents, then yes, this would give galvanic separation.

All the new generation TL series, including the SB 4000TL-20 has a RCMU, this unit is a Type B RCD and is able to distinguish between Earth Leakage and Earth Faults.

Any thoughts anyone?

Cheers

 

[yellowvanman]

Well I am arguing for something here I only half believe in (the DTI Guide) but here goes:
- the DTI guide says 10mm2

Can you point me to the correct page for that.

OK, found it!

 

[itty]

Well I am arguing for something here I only half believe in (the DTI Guide) but here goes:
- the DTI guide says 10mm2
- where you have PME then 7671 says 10mm2 for bonding
- if not PME then apply the rules to work out bonding conductor sizes

Of course if you do not believe it is a bonding conductor, but is a cpc then different answers will appear.
Regards
Bruce

This is the point I'm making. I'm playing devils advocate and the most resistance I encounter is a reluctant defence of the DTI.

The DTI is the only credible resource but the general consensus during canvassing was that it is outdated.

Also, BS7671 haven't seen fit to cover it in section 712. What does that tell us?

Cheers

 

[yellowvanman]

Still don't understand why 10mm is suggested.

Its not extraneous and not necessarily on a TNC-S system, and if we are comparing it with main bonding 6mm could be used on TNS and TT systems! Whilst supplementary bonding can use as small as 2.5!

Add to that if we are using a seperate stake the earth currents will be very small due to the high earth impedance!

 

[Easters]

Its easy to hide cable if you really want to.
I have bonded many frames and have dealt with it so the customer is happy but also tell them I is a part on the install that has to be done and I bet they wont moan at you for doing it the right way.

 

[edexlab]

The pdf you need to read is called Ableitstrom-UEN092510 this can be found on the knowledge base section under documents and tools

It is definitely necessary to bond the array I've tested between the bond cable and the rod on many TL jobs and found voltages as high as 116 volts maybe not enough to kill but could as previously mentioned cause a fall.

I went to SMA last year and this was discussed they explained it as parasitic capacitance ,basicly some of the AC voltage transfers across to the DC cables as there is no isolating transformer to prevent / limit this ,this voltage travels up to the array ,so if for example you were to be in contact with the ground via an aluminium ladder or working off scaffold (or even cleaning the array from the ground) and make contact with the array you will become the link in the circuit and receive a shock which varies from panel to panel depending on the substrate construction, by installing an earth spike or bonding back to the MET you reduce the PD which can occur
as has been mentioned before you should test any rod and ensure that the reading is at least within BS7671
personally I try to get them down to well below 100 ohms

As a matter of course I tell our clients to ensure the array is turned off when cleaning as any voltage present disappears when the system is off.

 

[itty]

Like to thank you all for the comments. Seems clear that the majority of posters favour bonding. I suspect the fact I have not received a hammering, speaks volumes....